Vectoring — a formal approach to tracking the sources and flow of pathogens in a facility

Pathogenic bacteria can infiltrate a facility from several different sources, including the external environment, people, equipment and raw materials. Once inside, pathogens can become established in harborage areas and carried to food production surfaces through a vector. Liquids, air, people and physical objects, such as carts or tools, are common vectors for pathogen transmission. It’s also not unusual for multiple vectors to contribute to the spread of pathogens in a facility.

The process of identifying the sources and flow of environmental pathogens is often called “vectoring.” This process typically involves a physical examination of an identified source and its surrounding area, as well as specific processes, such as the food production and sanitation efforts, involved in the area. Through a structured series of microbiological samples, sources and vectors of contamination can be identified and corrective actions implemented.

The United Fresh Produce Association recognizes vectoring as one of the common corrective actions taken by its members. In a 2017 report, it stated, “Increasing sampling around the area where a positive is found is a leading practice. Vectoring out in three dimensions, possibly to include zone 1 surfaces, should be done as part of an investigation.” (The report, “Industry Perspective on Environmental Monitoring for Listeria,” summarizes the dialogue during the United Fresh Food Safety & Technology Council meeting in January.)

So you’ve found Listeria…

In its 2014 report titled, “Listeria monocytogenes Guidance on Environmental Monitoring and Corrective Actions in At-Risk Foods,” the Grocery Manufacturers Association (GMA) recommends that facilities follow a structured program for investigations following a positive Listeria result.

Some of the GMA’s general suggestions for investigations include:

• Facilities should investigate and resample not just suspect sites, but also the surrounding areas and traffic pattern areas, for potential contamination sources (such as water leaks or maintenance activities). Sites should be picked judiciously — don’t necessarily use routine sample sites. During sampling, take care not to spread contaminants from suspect areas elsewhere in the plant.

• Increase sampling frequency until the problem is resolved. In order to resume the normal sampling schedule, at least three consecutive follow-up samples (the industry standard) of the problem site should be negative.

• You can use sampling throughout the facility to determine if Listeria has spread into another zone.

• Past data is your friend. By looking at old test results in the affected area, you can identify any trends or patterns. This can help you find the root cause of your positive results. Look at other data too, like test results from ATP or ACP testing and old maintenance records (including recent repairs, power outages, equipment changes, etc.).

• Take corrective action based on the likelihood that finished product is contaminated, given the location of the positive site in the plant environment. Document whatever actions you take.

• Don’t be afraid to bring in a third party expert if needed. A “fresh set of eyes” can be very helpful. Retraining employees might also be a good idea.

Investigating aside, what kind of corrective action should facilities take to limit the threat?

First, the organization suggests, limit access to the implicated area.

“Where necessary and feasible, limit traffic flows (including employees, materials and mobile equipment…) through the area, restrict fork truck movement, and redirect high risk traffic patterns from adjacent areas,” the report stated.

Conduct a visual inspection of equipment. Is there product buildup after cleaning? Any cracks, bad welds, or pooling water? Look at the condition of floors, walls, and ceilings. Replace or remodel any equipment that might be to blame.

The GMA suggests thoroughly cleaning and sanitizing the positive site and the nearby area, especially with heat (superheated steam, hot water or saturated steam). Could recontamination occur? Then conduct this process on a regular basis.